Auto merge of #13232 - jplatte:mbe-refactor, r=Veykril
Auto merge of #13232 - jplatte:mbe-refactor, r=Veykril

Refactor macro-by-example code

I had a look at the MBE code because of #7857. I found some easy readability wins, that might also _marginally_ improve perf.

rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer